Contact process



H. E. POTTS.- coumcr PROCESS. APPLICATION FILED JUNE 17. 1918.

Patented Mar. 30, 1920.

UNITED. STATES PATENT OFFICE.

HABbLD' E. POTTS, OFLIVERPOOL, ENGLAND, ASSIGNOR TO SIMON-CARVES, LTD., 01 MANCHESTER, ENGLAND.

l CONTACT rnocnss.

To all whom it may concern:

Be it known that I, HAROLD E. Porrs, a subject of the King of Great Britain, residing -in Liverpool, Lancashire 'county, England, have invented certain new and useful Improvements in Contact Processes,

of which 'the following is a full and clear specification.

'Although I-Ianisch' and Schroeder proposed to liquefy SO, from burner gases,and

then to mix the pure gas so obtained with air and catalyze it by platinum to" form S0 the whole'trend of development in practice has been alongthe lines of purifying burner gas by removing prejudicialimpurities and then converting the purified gas by platinum contact. 4

This method presents the disadvantage that the impurities are very difficult to remove and according to my invention I transfer the S0 from a stream of the impure burner gases to a stream of air in such manner that the S0 concentration in the air is of the same order of magnitude as that in the original burner gas, and I then dry this second stream and subject it to a The transference is efiected on the countor-current system and it is based on the principle that according to Henrys law the equilibrium between 'S-O in the liquid and gas phases is reversible and dependent only i on the temperature and acid concentration of the solution and on the partial pressure of SO in the gas. In other words the final equilibrium in a given system is the same at a given temperature and pressure if, say, one part by weight of S0 is present in a given volume of gas, which is then brought into contact with a given volume. of solution, or whether the same weight of S0 is present in the solution whic is then brought into contact with a given volume of air. 'aIt follows fromthis that'if a given volume of Specification of Letters Patent.

Application file d il'une 17, 1918. Serial No. 240,433.

burner gas containing, say, 7 of S0 is washed with water on the counter-current prlnciple, and this solution of S0 is then brought into contact with air on the countercurrent principle the enriched air leaving the saturated solution coming from the absorbers will-be of about the same strength (7% '80,) as the burner gas which was in final contact with the solution in the absorbers. This transference of SO maybe facilitated by raising the temperature of the liquid to be treated by air, say, 10 or 20 C. to reduce the solubility of gas, or by cooling the liquid in the absorbing system. This may be effected by heating or cooling the air and burner gas respectively or by arranging a cooler in circuit with the. liquid in the absorbers, and a heat interchanger (warmed by burner gases) in circuit with the system in which the air acts'on the, solution, which may be termed the evolving system.

In this way a gas is obtained which is eminently suitable for the contact process since the S0 from the original gas has been retained, while the undesirable impurities have been allowed to escape, or if they are absorbed inthe circulating liquid, they will no longer be in the same excessively finely distributed form so that they will not contaminate the stream of SO laden air; a

simple scrubber can be intercalated between the evolving system and the drying system.

It was proposed by Hanisch and Schroeder in 1883 (British Patent No. 2621 of 1883) to remove SO from furnace gases containing little SO, by cold water and to blow hot air into the solution to warm the solution by the burner gases to 100 C. and then to convert it into spray which was treated with 'hot air, an elaborate system of heat interchange was suggested to economize the heat involved in the alternate heating of the water to I00 C. and cooling it again.

The resultant gaswas stated'to contain 20% of S0 and to be suitable for the direct manufacture of sulfuric acid. No drying was described, and such gas is too strong for eflicient conversion by the contact process.

My invention is primarily for the treatment of"burner gases containing the normal amount of SO and its obj set is to separate the S0 not from products of. combustion of fuel so much as from finely lytic activity of platinum. My invention divided impuritiesand flue dust which would inhibitithecatafor its efiicacy on the distribution law, 1'. e.,.

on the fact that by the counter-current principle it is possible to obtain a transference of SO from one stream of (impure) gas to another stream of air at substantially the same concentration and at the same or almost the same temperature; it is therefore" based on an entirely different physico-chemical principle than,the above process which simpl de nds on the well known reduction of so ubillty of SO in water at a higher temperature.

It will be seen thatif the burner ses contain about 6 or 7% S0,, the resu ting as will contain about the same amount so t at it is suitable for conversion. It will liberate enough heat by the exothermic reac- A duced, and on the other hand, it will through the two absorbing tion.

2S0,0,=2SO,

to dispense with the necessity of heating the gases prior to conversion except by the well known heat interchange with the S0 pronot be so rich asto necessitate the employment of special cooling means for the contact chamher. With the contact chambers now usually employed, concentrations of 5% and 10% represent the approximate working limits. The strength of the gas may be controlled by adjusting the volume of air or the temperatures of the liquids in the absorbing and evolving systems so that there is the possi'bility of control of the SO, addition to the usual control at the burners.

percentage in The liquid in the absorbing and evolving system may be circulated by pumps, elevators, &c., over one, two or more towers in each system; and it is advisable to close in the whole of these systems to avoid loss of SO to the atmosphere.

The accompanying drawing shows by way of example, a diagrammatic flow sheet of the lant. 1 l

T e gases leave the burner B, passing through the dust chamber 1 and the. strong acid wash tower 2 (weak acid may be employed here if desired). The gases pass are discharged through the fan 5.

Air is pulled through the two evolving towers 5, 6, the scrubber 7, drying tower 8,

and scrubber 9 by the blower 10 after which it passes through a contact systemand an absorbing system of any known type.

The flow of water is shown by the dotted I lines.

towers 3, 4 and 7 The cold water is fed down'tower 4, to pump 15, then down tower 3 to tank 16, when it is saturated with S0,.- The liquor passes through heat interchange pipes 11 and flows through pump 17 and 'down' tower 6 to pump 14, then down tower 5 through cooler 12 and pump 13 to return again to the top of tower 4 and so. on cyclically.

I claim v 1. A process of making SO, which comrises transferring SO, from a stream of urner gas to a solvent liquid and then bringing air in contact with the liquid to remove the S0 without substantial increase 1 of SO, concentration in the air stream as compared with the burner gas, dryin said stream of air char (1 with S0, an converting said dried. 0 into SO by a-cata lyst;

2. A process of makin S0,. which comprises washi a stream 0 burner gas, tr'ansferring its, S 2 to a solvent liquid and then bringing air in contact with-the liquid to remove the S0 drying the'gas and converting SO into 'SO, by a catalyst.

3. A process of makin SO, which includes transferring S0, rom a stream of burner gas to a 'body' of water and then bringing air in contact with the water to remove the S0 these operations being conducted at a temperature not far removed from the temperature of the atmosphere.

4. A process of making SO, which includes transferring "SO from a stream of burner gas to a stream of air without substantial increase in SO concentration, alternately passing burner gas and air in contact with a solvent liquid which liquid is warmed by heat interchange prior to imparting its SO to the stream of air and cooled prior toabsorbing the S0 from the stream of burner gases.

5. A process of makin SO which includes transferring SO om a stream of burner to a stream of airlby. alternately passing urner gas and air in contact with a solvent liquid so that the concentration of SO in the stream of air is between about 5% and 10%.

6. A process of making S0 which comprises transferring SO 'from a stream of burner gas containing in the neighborhood of 7% of S0, to a stream of air which after 

